Liquid crystal display apparatus

ABSTRACT

In a liquid crystal display device including a liquid crystal display panel ( 10 ) including a liquid crystal layer ( 3 ) sandwiched between a first substrate ( 1 ) and a second substrate ( 2 ) having transparent electrodes ( 5, 6 ) on inner surfaces opposing to each other, the film thickness of at least one of the transparent electrodes ( 5, 6 ) formed on the first and second substrates ( 1, 2 ) is set so that light passing through the transparent electrode and exhibiting a maximum transmittance has a color within either a region defined by an x value of 0.22 to 0.28 and a y value of 0.21 to 0.31 or a region defined by an x value of 0.28 to 0.34 and a y value of 0.22 to 0.35 in a chromaticity diagram of a CIE 1931 color system using a white light source. This reduces coloring irregularities due to a film thickness error caused during manufacturing of the transparent electrodes to enable performance of uniform display.

TECHNICAL FIELD

The invention relates to a liquid crystal display device which includesa liquid crystal display panel including a liquid crystal layersandwiched between a pair of substrates having transparent electrodesformed respectively on inner surfaces opposing to each other.

BACKGROUND TECHNOLOGY

Conventionally, liquid crystal display devices which perform imagedisplay through use of liquid crystal have been extensively used in awide range from small portable devices such as timepieces, personaldigital assistants, cellular phones, and so on to relatively largedisplay devices such as display televisions and so on.

The liquid crystal display device as described above includes a liquidcrystal display panel made by bonding together a pair of substrates eachhaving transparent electrodes formed on one surface, in such a mannerthat the transparent electrodes are opposed to each other, and includinga liquid crystal layer sealed in the gap therebetween.

In performing display, a display signal is applied between the opposingtransparent electrodes to apply voltage to the liquid crystal layer,thereby changing its optical property to change transmission, scatteringand polarization properties and so on of light for each predeterminedregion. Such a liquid crystal display panel is combined with opticalmembers such as a polarizing film, a retardation film, a reflector, andso on, thereby allowing the optical change of the liquid crystal layerto be recognized as brightness/darkness, scattering/transmission, or thelike of display. If a color filter is additionally combined therewith,color display is also made possible.

The liquid crystal display device as described above does not emit lightitself and therefore utilizes light which passes through liquid crystalcells to perform display.

The ways of utilizing light include, for example, a reflection type thatutilizes external light incident from the visible side and atransmission type that utilizes a backlight that is an auxiliary lightsource provided on the opposite side to the visible side of the liquidcrystal display panel, and a transflective liquid crystal display devicecapable of utilizing both of them is also known.

Incidentally, display in the liquid crystal display device is morepreferably uniform as much as possible other than changes such asbrightness/darkness, scattering/transmission, or the like which isgenerated by optical change in the liquid crystal layer. On the otherhand, the liquid crystal display devices of both the transmission-typeand the reflection-type perform display by utilizing light passingthrough the liquid crystal display panel, and therefore the display isnecessarily affected not only by the liquid crystal layer but also bythe optical members in the liquid crystal display panel.

As the material of the transparent electrodes essential for the liquidcrystal display panel, ITO (Indium Tin Oxide) is mainly used, which willbe an optical member affecting display because ITO is different inrefractive index from the substrate. When ITO films, for example, withvarious film thicknesses are formed on a glass substrate and coloringthereof is measured, coloring in various colors in accordance with thefilm thickness appear as shown in the chromaticity diagram in FIG. 7.Therefore, nonuniform film thickness will cause coloring irregularitiesin display. It should be noted that FIG. 7 is obtained by plotting, inthe chromaticity diagram of the CIE (Commission Internationale deI'Eclairage) 1931 color system, colors of transmitted light when ITOfilms having a film thickness of 0 to 400 nm are formed, in incrementsof 10 nm, on the glass substrate via a silicon dioxide (SiO₂) filmhaving a film thickness of 25 nm and light generated by a D65 lightsource that is a white light source close to sunlight is appliedthereto.

The transparent electrode made of ITO, however, desirably has a filmthickness on the order of several hundreds Å to several thousands Å fromits necessary resistance value, but it is difficult to form an ITO filmhaving a film thickness of this level in terms of cost. Accordingly,there has been a problem that coloring with irregularities due to thetransparent electrode appears so that sufficiently uniform displaycannot be performed in a conventional liquid crystal display device.

In addition, to perform clear display, occurrence of coloring itself isnot preferable. In particular, in the case of performing color displayusing a color filter, there has been a problem that the display colorcreated by the color filter cannot be accurately set when coloring iscaused by other optical members.

An object of the invention is to solve the above-described problems soas to reduce the coloring irregularities and enable performance ofuniform display in a liquid crystal display device. Further, anotherobject is to enable performance of display without coloring.

DISCLOSURE OF THE INVENTION

In order to achieve the above objects, the invention is a liquid crystaldisplay device including a liquid crystal display panel including aliquid crystal layer sandwiched between a first substrate on a visibleside and a second substrate on an opposite side to the visible sidehaving transparent electrodes on inner surfaces opposing to each other,wherein a transfiective film formed of a dielectric multilayered filmmade by alternately layering a high refractive index film and a lowrefractive index film is provided between the second substrate and thetransparent electrode on the second substrate, wherein at least one ofthe transparent electrodes formed on the first and second substrates iscolored, and wherein spectroscopic characteristics within a visibleregion of a reflected light or a transmitted light by the transflectivefilm are almost flat through correction of coloring of light transmittedthrough the at least one transparent electrode.

In the liquid crystal display device described above, it is preferablethat a film thickness of the at least one of transparent electrodes isset so that light passing through the transparent electrode andexhibiting a maximum transmittance has a color within either a regiondefined by an x value of 0.22 to 0.28 and a y value of 0.21 to 0.31 or aregion defined by an x value of 0.28 to 0.34 and a y value of 0.22 to0.35 in a chromaticity diagram of a CIE 1931 color system using a whitelight source.

Further, it is preferable that a first light control layer havingoptical anisotropy is provided on the opposite side to the liquidcrystal layer of the first substrate, and the first light control layerhas a characteristic of correcting coloring of light emitted from theliquid crystal display panel to make spectroscopic characteristicsthereof within a visible region almost flat.

Further, it is preferable that an auxiliary light source placed on theopposite side to the liquid crystal layer of the second substrate, and asecond light control layer having optical anisotropy placed between theauxiliary light source and the second substrate, are providedrespectively, wherein either or both of the auxiliary light source andthe second light control layer has/have a characteristic of correctingcoloring of transmitting light emitted from a light source andtransmitting through the liquid crystal display panel and the first 10light control layer to make spectroscopic characteristics within thevisible region of the transmitting light almost flat.

Besides, it is preferable that the at least one transparent electrode isa transparent electrode formed on the second substrate.

Otherwise, it is preferable that the at least one transparent electrodeis 1600 Å to 2000 Å in film thickness.

Alternatively, it is also adoptable that the at least one transparentelectrode is 2600 Å to 3000 Å in film thickness.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view schematically showing a configurationof a liquid crystal display device of a first embodiment of theinvention;

FIG. 2 is a cross-sectional view schematically showing a configurationof a liquid crystal display device of a second embodiment of theinvention;

FIG. 3 is a diagram showing the planar positional relationship amongmembers in the liquid crystal display device;

FIG. 4 is a similar diagram showing the planar positional relationshipbetween other members;

FIG. 5 is a graph showing spectroscopic characteristics of a dielectricmultilayered film used in the liquid crystal display device;

FIG. 6 is a similar graph showing spectroscopic characteristics in acase in which a transparent conductive film made of ITO is formed on adielectric multilayered film; and

FIG. 7 is a diagram made by plotting in a chromaticity diagram of a CIE1931 color system colors of transmitted light when ITO films withvarious film thicknesses are formed on a glass substrate via a SiO₂film.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the invention will be described below withreference to the drawings.

First Embodiment: FIG. 1 and FIG. 7

First, a first embodiment of a liquid crystal display device of theinvention will be described. FIG. 1 is a cross-sectional view showing aconfiguration of the liquid crystal display device. Note that, in thisdrawing, respective constituting members are shown with theirthicknesses and spacing therebetween substantially enlarged.

As shown in FIG. 1, this liquid crystal display device comprises aliquid crystal display panel 10; a first polarizing film 12 placed onits visible side (the upper side in the drawing); a second polarizingfilm 14 placed on the opposite side to the visible side (the lower sidein the drawing) of the liquid crystal display panel 10; a reflectivefilm 16 placed on the opposite side to the visible side of the secondpolarizing film 14; and a liquid crystal driving IC 22 provided on asecond substrate 2. It is a reflection-type liquid crystal displaydevice utilizing external light that is incident from the visible side.

The liquid crystal display panel 10 is made by bonding together a firstsubstrate 1 and the second substrate 2, which are made of transparentinsulation material such as glass respectively, with a sealant 4provided at their peripheries, and has a liquid crystal layer 3sandwiched therebetween. On opposing inner surfaces of the first andsecond substrates 1 and 2, first and second electrodes 5 and 6 made ofindium tin oxide (ITO) or the like are formed, respectively, in stripesperpendicular to each other, so that each portion where the first andsecond electrodes 5 and 6 planarly overlap each other forms a pixelportion.

The liquid crystal layer 3 is composed of twisted nematic (TN) liquidcrystal with a twist angle of 90 degrees. Further, a not-shown alignmentfilm is provided on each of the substrates 1 and 2 and electrodes 5 and6 on the side in contact with the liquid crystal layer 3 and subjectedto alignment treatment so that liquid crystal molecules are aligned inpredetermined directions.

The first polarizing film 12 placed on the visible side of the liquidcrystal display panel 10, which is an absorption-type polarizing film,is a member in a shape of a sheet which transmits linearly polarizedlight in the direction parallel to the transmission axis and absorbslinearly polarized light in the direction of the absorption axisorthogonal to the transmission axis. The second polarizing film 14placed on the opposite side to the visible side of the liquid crystaldisplay panel 10 is also the absorption-type polarizing film similar tothe first polarizing film 12. The first polarizing film 12 constitutes afirst light control layer and the second polarizing film 14 constitutesa second light control layer here.

The reflective film 16 is a mirror-surface reflective film made of metalsuch as silver or aluminum and reflects almost all of incident lightwithin the overall wavelength range of visible light.

In this device, the first polarizing film 12 is placed such that itstransmission axis is parallel to the direction of the long axis of theliquid crystal molecules on the visible side in the liquid crystal layer3 of the liquid crystal display panel 10. Besides, the second polarizingfilm 14 is placed such that its transmission axis is parallel to thedirection of the long axis of the liquid crystal molecules on theopposite side to the visible side in the liquid crystal layer 3 of theliquid crystal display panel 10. Accordingly, the transmission axis ofthe first polarizing film 12 and the transmission axis of the secondpolarizing film 14 are orthogonal to each other.

The directions of the stripes in the first polarizing film 12 and thesecond polarizing film 14 in FIG. 1 show the directions of therespective transmission axes, the horizontal stripes in the firstpolarizing film 12 showing the direction parallel to the paper surfaceand the vertical stripes in the second polarizing film 14 showing thedirection perpendicular to the paper surface.

The liquid crystal display device thus configured can perform display byapplying driving signals from the liquid crystal driving IC (integratedcircuit) 22 to the first and second electrodes 5 and 6 via not-shownconnecting electrodes and controlling application or non-application ofvoltage to each pixel portion to change optical characteristics of theliquid crystal layer 3 for each pixel portion. Note that the connectionfrom the liquid crystal driving IC 22 to the first electrodes 5 on thefirst substrate 1 can be established by forming at least a part of thesealant 4 by using of an anisotropic conductive adhesive that is made bymixing conductive particles into an insulating adhesive and electricallyconnecting the connecting electrode formed on the first substrate andthe connecting electrode formed on the second substrate 2 through use ofthis anisotropic conductive adhesive.

The principle of display by this liquid crystal display panel will befurther described here.

Half of the light, which is made incident on the liquid crystal displaydevice from the visible side (the upper side in the drawing), isabsorbed by the first polarizing film 12, and the other half istransmitted through the first polarizing film 12 to become linearlypolarized light in the direction parallel to the paper surface and madeincident on the liquid crystal display panel 10. The light then passesthrough members such as the first substrate 1, the first electrode 5,the liquid crystal layer 3, the second electrode 6, the second substrate2, and so on and exits to the second polarizing film 14 side.

Since the liquid crystal layer 3 of the liquid crystal display panel 10is the liquid crystal layer with a twist angle of 90° in which the longaxis direction of the liquid crystal molecules on the visible side isparallel to the transmission axis of the first polarizing film 12 asdescribed above, the linearly polarized light transmitted through thefirst polarizing film 12 passes through the liquid crystal display panel10 with its polarization direction twisted 90 degrees to becomeperpendicular to the paper surface during the passing at a portion inthe OFF state where no voltage is applied to the liquid crystal layer 3,and is made incident on the second polarizing film 14. Therefore, thelinearly polarized light has the polarization direction that is the sameas the direction of the transmission axis of the second polarizing film14, and is therefore transmitted through the second polarizing film 14and reflected by the reflective film 16 on the opposite side to thevisible side. The light then passes through the path reversed to thatduring the incidence and exits to the visible side, so that the portionin the OFF state is recognized as display in mirror tone as seen fromthe visible side.

On the other hand, at a portion in the ON state where voltage is appliedto the liquid crystal layer 3, the liquid crystal molecules rise to losethe twist, so that the linearly polarized light transmitted through thefirst polarizing film 12 passes through the liquid crystal display panel10 without being twisted, and is made incident on the second polarizingfilm 14 with its polarization direction being kept in the directionparallel to the paper surface. Accordingly, since the polarizationdirection is orthogonal to the direction of the transmission axis of thesecond polarizing film 14, the linearly polarized light is absorbed bythe second polarizing film 14. As a result, the reflected light hardlyexits to the visible side, so that the portion in the ON state isrecognized as black display as seen from the visible side.

As described above, in this liquid crystal display device, display canbe performed, switched between the mirror tone and black, by controllingthe application and non-application of voltage to the liquid crystallayer 3 in a unit of pixel.

Next, the film thickness of the electrode that is a characteristic ofthe invention will be described.

In this liquid crystal display device, the film thickness of the secondelectrode 6 formed on the second substrate 2 is set to a film thicknessso that the color of light passing through the second electrode 6becomes a color in the blue region within the luminosity range.

Since ITO used as the material of the second electrode 6 is different inrefractive index from the substrate as described in BackgroundTechnology section, if the second electrode 6 is formed on the secondsubstrate 2 that is a glass substrate, light passing through thesemembers is subjected to coloring in various colors as shown in FIG. 7 inaccordance with the film thickness of ITO used as the material of thesecond electrode 6. Note that FIG. 7 shows coloring when the ITO film isformed on the glass substrate via the SiO₂ film as described above, andthe coloring is not different therefrom even though the ITO film isformed directly on the glass substrate.

On the other hand, the film thickness of the transparent electrode isdesirably on the order of several hundreds Å to several thousands Å froma necessary resistance value, but when the ITO film with the filmthickness of this level is desired to be formed at a low cost, an erroron the order of ±10% from the target film thickness will occur.Accordingly, to eliminate irregularities of coloring due to the secondelectrode 6, it is necessary to set the film thickness in a range inwhich color does not greatly change even when the error at this leveloccurs in the film thickness.

Referring again to the plot in the chromaticity diagram in FIG. 7 here,it is found that the change in coloration of coloring when the filmthickness is changed is relatively small in the case where the color ofthe transmitted light is a color within either the region defined by anx value of 0.22 to 0.28 and a y value of 0.21 to 0.31 (blue) or theregion defined by an x value of 0.28 to 0.34 and a y value of 0.22 to0.35 (purple to red), which are within the luminosity range (visibleregion).

In particular, it is found that the change in coloration of the coloringwhen the film thickness is changed can be made smaller when theelectrode is formed in a film thickness of 1600 Å to 2000 Å so that thecolor of the transmitted light is a color within the blue region of theluminosity range and when the electrode is formed in a film thickness of2600 Å to 3000 Å so that the color of the transmitted light is a colorwithin the red region of the luminosity range. However, since with anincrease in the film thickness of the electrode the transmittanceaccordingly decreases to cause display to be dark, and the manufacturingerror in terms of film thickness also becomes larger, the former is morepreferable in consideration of this viewpoint as well.

Although the film thickness of the second electrode 6 is set to 1800 Åso that the color of light passing through the second electrode 6 is acolor in the blue region within the luminosity range to thereby reducethe coloring irregularities of light passing through the secondelectrode 6 in this liquid crystal display device, the same effect canbe obtained even when the film thickness is set so that the color is acolor in the region of purple or red.

This arrangement enables uniform display on the entire surface of thedisplay region (the region where the electrodes are formed) of theliquid crystal display device. Further, even if the film thickness ofthe transparent electrode varies, for example, ±10% due to themanufacturing error, among many liquid crystal display devicesmanufactured, the coloring of the transparent electrode to which theinvention is applied hardly varies, so that the display quality of theliquid crystal display device can be kept almost uniform.

Besides, when the coloring itself is desired to be eliminated, a colorfilter or the like of a color in complementary relation to the coloradded by the second electrode 6 can be provided to eliminate thecoloring with ease. Further, in performing color display using colorfilters of red, (R), green (G), blue (B), and so on, setting of opticalcharacteristics of each color filter for displaying an arbitrary colorcan be performed easily and accurately.

It should be noted that the setting of the film thicknesses of theelectrodes on both the substrates as described above allows furtherimprovement in terms of reduction in color irregularities, but the filmthickness of the electrode to be formed on one of the first and secondsubstrates 1 and 2 may be more effective in improving the displayquality when it is set with emphasis placed on the characteristics suchas the resistance value or the like of wiring pull around in the liquidcrystal display panel 10 than when it is set at request from opticalcharacteristics as described above. Hence, in this liquid crystaldisplay device, the film thickness of the first electrode 5 is set to be2200 Å with emphasis placed on the characteristics such as theresistance value or the like. The set film thickness enables the sheetresistance of ITO to be 10/sq that is the level at which there is noproblem in terms of wiring resistance.

This arrangement can also provide sufficient effects of reducing thecoloring irregularities by setting the film thickness of at least one ofthe transparent electrodes to be formed on the first and secondsubstrates so that the color of light passing through the transparentelectrode is a color in the region of blue, purple or red within theluminosity range.

It is needless to say that the same effects are provided even when thefilm thicknesses of the first and second electrodes 5 and 6 are reversedin this liquid crystal display device. Besides, while the example of thereflection-type liquid crystal display device using the twoabsorption-type polarizing films 12 and 14, the liquid crystal displaypanel 10 using the TN liquid crystal, and the reflective film 16 isdescribed here, the invention is of course applicable to various liquidcrystal display devices such as a transmission-type liquid crystaldisplay device provided with an auxiliary light source in place of thereflective film 16, a liquid crystal display device using STN liquidcrystal in place of the TN liquid crystal, a single polarizing film-typeliquid crystal display device using a retardation film, an activematrix-type liquid crystal display device using thin film diodes or thinfilm transistors, a liquid crystal display device using scattering-typeliquid crystal, and so on.

Second Embodiment: FIG. 2 to FIG. 5

Next, a second embodiment of a liquid crystal display device of theinvention will be described. FIG. 2 is a cross-sectional viewschematically showing a configuration of the liquid crystal displaydevice, FIG. 3 and FIG. 4 are diagrams each showing the planarpositional relationship among members in the liquid crystal displaydevice, and FIG. 5 is a graph showing spectroscopic characteristics of adielectric multilayered film used in the liquid crystal display device.Note that, in FIG. 2, respective constituting members are shown withtheir thicknesses and spacing therebetween substantially enlarged.

As shown in FIG. 2, this liquid crystal display device comprises aliquid crystal display panel 10′; a first retardation film 15 and afirst polarizing film 12 which are sequentially placed on its visibleside (the upper side in the drawing); a second retardation film 17, asecond polarizing film 14, and a backlight 20 that is an auxiliary lightsource, which are sequentially placed on the opposite side to thevisible side of the liquid crystal display panel 10′; and a liquidcrystal driving IC 22 placed on a second substrate 2 of the liquidcrystal display panel 10′.

The liquid crystal display panel 10′ has a configuration in which afirst substrate 1 and the second substrate 2, which are made of a glassplate with a thickness of 0.5 mm respectively, are bonded together witha sealant 4 provided at their peripheries, and a liquid crystal layer13, which is composed of super twisted nematic (STN) liquid crystalaligned at a twist angle of 240° counterclockwise, fills a gaptherebetween and sandwiched by the substrates.

Further, a transflective film 18, which is composed of a dielectricmultilayered film made by alternately layering a high refractive indexlayer and a low refractive index layer, is formed as a reflective filmon the entire surface on the visible side of the second substrate 2, andsecond electrodes 6 are formed directly thereon.

On an inner surface of the first substrate 1, first electrodes 5 areformed. The first and second electrodes 5 and 6 are both made of anindium tin oxide (ITO) film that is a transparent conductive film instripes perpendicular to each other, so that each portion where thefirst electrode 5 and the electrode 6 planarly overlap each other formsa pixel portion.

An alignment film is formed on the first electrodes 5 including theinner surface of the first substrate 1, and on the second electrodes 6including the transflective film 18, respectively, but theirillustrations are omitted.

The transflective film 18 provided in this liquid crystal display devicewill be described in detail here.

The transflective film 18 is formed by alternately layering a highrefractive index layer composed of a TiO₂ film having a refractive indexof about 2.6 and a low refractive index layer composed of a SiO₂ filmhaving a refractive index of about 1.2, which are in film thicknesses asshown in Table 1, and the total thickness is 6850 Å.

TABLE 1 Material Film Thickness (Å) Visible side 1 SiO₂ 1200 2 TiO₂ 8803 SiO₂ 830 4 TiO₂ 650 5 SiO₂ 980 6 TiO₂ 500 7 SiO₂ 420 8 TiO₂ 400 9 SiO₂840 10 TiO₂ 150 Second substrate 2 side

The dielectric multilayered film thus formed functions as atransflective film which transmits about 30% of incident light andreflects the other. It was found from the experiment by the presentinventors that there is no remarkable peak within the visible regionwhen the transmittance of light where the dielectric multilayered filmas described above is formed on a glass substrate is plotted withrespect to the wavelength of light as shown in FIG. 5, the spectroscopiccharacteristics of the transmitted light within the visible region beingthus almost flat, and as a result, the dielectric multilayered film isan achromatic film. Since the reflected light is the other than thetransmitted light, the spectroscopic characteristics of the reflectedlight within the visible region also necessarily become almost flat, sothat it is achromatic reflected light. Note that colors generally usedfor display in the liquid crystal display device are colors havingwavelengths ranging from 450 nm to 650 nm, and therefore the visibleregion is defined as this range in this description.

Since the dielectric multilayered film as described above is aninsulator, the dielectric multilayered film when used as thetransflective film 18 causes no short circuit between electrodes evenwhen the electrodes are formed directly on the transflective film 18 viano protective film. Further, the dielectric multilayered film is alsochemically stable and thus allows treatment under high humidity or highpressure conditions or use of strongly corrosive etchant when memberssuch as electrodes, alignment films, color filters for performance ofcolor display, and so on are formed, so that these members can be formedat low cost, resulting in reduced cost of the device.

However, when the dielectric multilayered film as described above isused as the transflective film 18 and the second electrodes 6 are formeddirectly thereon, there arises a problem of irregular coloring due tovariation in the film thickness of the electrode, in particular, asdescribed in Background Technology section and the first embodiment.

It is known that the greater the difference in refractive index betweenadjacent optical members is, the more remarkable the coloring becomes.As compared to the case in which the electrode made of the ITO film isformed directly on the glass substrate as in the first embodiment, inthe case in which the electrode made of the ITO film is formed directlyon the dielectric multilayered film as in this liquid crystal displaydevice, the difference in refractive index between these members isgreater and the coloring accordingly becomes more remarkable, resultingin more conspicuous irregularities therein as a matter of course. Morespecifically, the refractive index of glass is about 1.5 and therefractive index of ITO is about 1.7 to about 1.8, so that thedifference in refractive index between these members is on the order of0.2 to 0.3, while the refractive index of SiO₂ is about 1.2 and therefractive index of TiO₂ is about 2.6 as described above, so that thedifference in refractive index between these and ITO is on the order of0.5 to 0.6 or on the order of 0.8 to 0.9, and the coloring of ITObecomes accordingly more remarkable.

Besides, since the glass substrate transmits nearly 100% of light,coloring irregularities due to the variation in film thickness of ITOare masked with an abundance of light to become relativelyinconspicuous. Besides, when a metal thin film is used as thetransflective film, influence of coloring due to absorption of lightwith a specific wavelength by the metal thin film is great, so that thecoloring irregularities due to the variation in film thickness of ITOalso become relatively inconspicuous.

The dielectric multilayered film used here, however, utilizes only about30% of the quantity of the incident light during transmission and about70% of the quantity of the incident light during reflection, and hasspectroscopic characteristics within the visible region which are almostflat characteristics, so that display will be greatly affected bycoloring irregularities of ITO unlike the above-described case.Therefore, it is particularly important to reduce the coloringirregularities due to the variation in film thickness of ITO in theliquid crystal display device using the dielectric multilayered film asthe transflective film as in this liquid crystal display device.

Hence, the film thickness of the second electrode 6 made of ITO is setto 1800 Å so that the color of light passing through the secondelectrode 6 is a color in the blue region within the luminous range asin the first embodiment to thereby decrease the colorationirregularities due to an error in film thickness of ITO caused duringmanufacturing. In addition to this, when the film thickness of thesecond electrode 6 is set to the value which is described in the firstembodiment, the same effect can be obtained.

Besides, the film thickness of the first electrode 5 formed on the firstsubstrate 1 is set to 2200 Å as in the first embodiment.

As for this point, as described in the first embodiment, the filmthickness of one of the first electrode 5 and the second electrode 6 isoften more effective in improving the display quality when it is setwith emphasis placed on the characteristics such as the resistance valueor the like. In addition, in the liquid crystal display device, sincecolor irregularities due to the variation in the film thickness appearmore remarkably by the second electrode 6 formed on the dielectricmultilayered film than by the first electrode 5 formed on the glasssubstrate, the film thickness of the second electrode 6 is moreeffective in reducing the color irregularities as a whole when it is setat request from optical characteristics.

Note that some effect can be obtained even when the film thickness ofthe first electrode 5 is set at request from optical characteristics.

The description on the other members in the liquid crystal displaydevice will be continued.

The first polarizing film 12 and the first retardation film 15 which areplaced on the visible side of the liquid crystal display panel 10′ arebonded together with an acrylic adhesive into one body and attached tothe outer surface of the first substrate 1 of the liquid crystal displaypanel 10′ with an acrylic adhesive. These first polarizing film 12 andthe first retardation film 15 constitute a first light control layerhaving optical anisotropy.

The first polarizing film 12 is an absorption-type polarizing filmsimilar to that in the first embodiment.

The first retardation film 15 is a transparent film with a thickness ofabout 70 μm made by stretching polycarbonate (PC) and has a retardationvalue R of 0.39 μm at a wavelength of 0.55 μm. As the first retardationfilm 15, a so-called Z-type retardation film which has a relation ofnx>nz>ny where the refractive index in the slow axis direction isdefined as nx, the refractive index in the direction orthogonal to theslow axis is defined as ny, and the refractive index in the thicknessdirection is defined as nz is used.

On the other hand, the second polarizing film 14 and the secondretardation film 17 which are placed on the opposite side to the visibleside of the liquid crystal display panel 10′ are also bonded togetherwith an acrylic adhesive into one body and attached to the outer surfaceof the second substrate 2 of the liquid crystal display panel 10′. Thesesecond polarizing film 14 and the second retardation film 17 constitutea second light control layer having optical anisotropy.

The second retardation film 17, which is one with a thickness of about70 μm made by stretching polycarbonate, is a quarter-wave plate having aretardation value F3=0.14 μm at a wavelength of 0.55 μm.

The second polarizing film 14 is an absorption-type polarizing filmsimilar to that in the first embodiment.

As the backlight 20, it is possible to use a light guide film with afluorescent light or LED attached thereto or an electro luminescence(EL) plate, and an EL plate with a thickness of about 1 mm and whiteluminescent color is used in this embodiment.

Next, the planar positional relationship among these constitutingmembers will be described using FIG. 3 and FIG. 4 as well.

Alignment films (not shown) are formed on the surfaces of the firstelectrodes 5 and the second electrodes 6 of the liquid crystal displaydevice 10′ shown in FIG. 2, and the one on the second substrate 2 sideis subjected to rubbing treatment in the upper-right 30° direction withrespect to the horizontal axis so that a lower molecular alignmentdirection 13 a of liquid crystal in the liquid crystal layer 13 is +30°,and the other on the first substrate 1 side is subjected to rubbingtreatment in the lower-right 30° direction so that an upper molecularalignment direction 13 b of liquid crystal in the liquid crystal layer13 is −30°.

An optical rotary material that is called a chiral material is added tothe nematic liquid crystal with a viscosity of 20 cp which constitutesthe liquid crystal layer 13, and a twist pitch P is adjusted to be 11 μmso that the twist direction is counterclockwise and a twist angle is240°.

The difference Δn in birefringence of the nematic liquid crystal in useis 0.131, and the cell gap d that is the gap between the first substrate1 and the second substrate 2 is set to 5.8 μm. Therefore, a Δnd value Rswhich is expressed by the product of the difference Δn in birefringenceof the nematic liquid crystal and the cell gap d, representing thebirefringence of the liquid crystal display panel 10′, is 0.76 μm.

An absorption axis 12 a of the first polarizing film 12 is placed, asshown in FIG. 4, at +30° with respect to the horizontal axis. A slowaxis 15 a of the first retardation film 15 is placed at +65° withrespect to the horizontal axis. This results in a crossing angle αbetween the absorption axis 12 a of the first polarizing film 12 and theslow axis 15 a of the first retardation film 15 of 35°.

A slow axis 17 a of the second retardation film 17 which is placed onthe opposite side to the visible side of the liquid crystal displaypanel 10′ is placed, as shown in FIG. 3, at +75° with respect to thehorizontal axis, and an absorption axis 14 a of the second polarizingfilm 14 is placed at −60° with respect to the horizontal axis, so as tobe orthogonal to the absorption axis 12 a of the first polarizing film12.

Display operation of the liquid crystal display device in thisembodiment will be described here.

This liquid crystal display device can also perform display, as in thefirst embodiment, by applying driving signals from the liquid crystaldriving IC 22 to the first and second electrodes 5 an 6 via not-shownconnecting electrodes and controlling application or non-application ofvoltage to each pixel portion to change optical characteristics of theliquid crystal layer 3 for each pixel portion. The way of connection isalso the same as in the first embodiment.

The linearly polarized light incident on the liquid crystal displaydevice from the visible side and passing through the first polarizingfilm 12 is transmitted through the first retardation film 15 and theliquid crystal layer 13 of the liquid crystal display panel 10′, wherebylight with all wavelengths within the visible region become circularlypolarized light at portions where no voltage is applied to the liquidcrystal layer 13. Since the second electrode 6 and the not-shownprotective layer have no birefringency, the circularly polarized lightreaches the transflective film 18 with the polarization state unchanged.

The circularly polarized light reflected by the transflective film 18 istransmitted again through the liquid crystal layer 13 and the firstretardation film 15 to be returned to the linearly polarized light withthe polarization direction rotated 90° and all absorbed by the firstpolarizing film 12, so that the reflectance is low within almost all thevisible region, leading to excellent black display.

When a predetermined voltage is applied to the liquid crystal layer 13,the nematic liquid crystal molecules rise to decrease the substantialΔnd value of the liquid crystal display panel 10′. Accordingly, thelinearly polarized light incident and passing through the firstpolarizing film 12 is not brought into fully circularly polarized lighteven after transmitted through the first retardation film 15 and theliquid crystal layer 13 but into elliptically polarized light orlinearly polarized light.

Where the amount of birefringence occurring in the liquid crystal layer13 due to the application of voltage is set to an equivalence of aquarter wavelength, the linearly polarized light incident through thefirst polarizing film 12 and reflected by the transflective film 18returns as it is without rotation, so that the reflectance is highwithin almost all the visible region, leading to bright and excellentwhite display in mirror tone.

On the other hand, in the case of transmission display where thebacklight 20 is turned on, the light emitted from the backlight 20passes through the second polarizing film 14 to become linearlypolarized light. This linearly polarized light is made incident at anangle of 45° with respect to the slow axis 17 a of the secondretardation film 17 to become circularly polarized light. Then, about70% of the light is reflected by the transfiective film 18 but the other30% of the light is transmitted therethrough.

In the region where no voltage is applied to the liquid crystal layer13, the resultant retardation value of the first retardation film 15 andthe liquid crystal display panel 10′ is a quarter wavelength at almostall wavelengths. Therefore, when the members are placed as in thisliquid crystal display device, subtraction of the retardation generatedby the second retardation film 17 from the resultant retardation of theliquid crystal display panel 10′ and the first retardation film 15results in zero, so that the light becomes linearly polarized light inthe polarization direction parallel to the transmission axis of thesecond polarizing film 14 and exits from the first retardation film 15and is made incident on the first polarizing film 12.

Since the absorption axis 12 a of the first polarizing film 12 and theabsorption axis 14 a of the second polarizing film 14 are orthogonal toeach other (therefore, the transmission axes thereof are also orthogonalto each other), the incident light cannot be transmitted through thefirst polarizing film 12, leading to black display.

When a predetermined voltage is applied to the liquid crystal layer 13,the nematic liquid crystal molecules rise to decrease the substantialΔnd value of the liquid crystal display panel 10′. Therefore, thelinearly polarized light emitted from the backlight 20 and passingthrough the second polarizing film 14 is brought into circularlypolarized light after passing through the second retardation film 17 andinto elliptically polarized light or linearly polarized light aftertransmitted through the liquid crystal layer 13 and the firstretardation film 15.

Where the retardation occurring in the liquid crystal display panel 10′due to the application of voltage is set to a quarter wavelength, thelinearly polarized light incident through the second polarizing film 14is further transmitted through the first retardation film 15 with thepolarization direction being rotated by 90° and thus transmitted throughthe first polarizing film 12, leading to excellent white display.

As described above, this liquid crystal display device can performdisplay while switching between mirror tone and black when utilizinglight incident from the visible side, and while switching between whiteand black when utilizing light of the backlight 20, by controllingapplication or non-application of voltage to the liquid crystal layer 3in each pixel.

In addition, while the manufacturing cost of the liquid crystal displaydevice can be reduced as described above because of use of thedielectric multilayered film as the transflective film 18, display canbe uniformly performed on the entire surface within the display region(the region where the electrodes are formed) of the liquid crystaldisplay device since coloring irregularities of light passing throughthe first electrode 5 are reduced by setting the film thickness of thefirst electrode 5 to 1800 Å so that the color of light passing throughthe first electrode 5 is a color in the blue region within theluminosity range. As described above, this effect is particularlyremarkable in the configuration in which the transparent electrodes areformed directly on the dielectric multilayered film as in this liquidcrystal display device.

That the same effect can be obtained even when the color of lightpassing trough the first electrode 5 is set to a color in the purple orred region within the luminosity range and that this invention isapplicable to other various liquid crystal display devices are the sameas in the first embodiment.

Modification of Second Embodiment: FIG. 6

Next, a modification of the second embodiment will be described. FIG. 6is a graph showing spectroscopic characteristics of a case in which atransparent conductive film made of ITO is formed on a dielectricmultilayered film used in this liquid crystal display device.

From the simulation by the present inventors on the above-describedliquid crystal display device of the second embodiment, the relationbetween the wavelength and transmittance in the case where thedielectric multilayered film used in this liquid crystal display deviceand an ITO film with a film thickness of 1800 Å are sequentially formedon a glass substrate and light generated by a D65 light source isapplied thereto is as shown in FIG. 6.

A layered body of the dielectric multilayered film and the ITO filmhaving such spectroscopic transmittance characteristics when formed onthe glass substrate exhibits, by calculation, pale red with L* of 54.5,a* of 16.0, and b* of 6.72 in the CIE 1976 color system (exhibitscomplementary color to this color in the reflection case). This is ingood agreement with the coloring of an actually fabricated liquidcrystal display device. This coloring is different from that when an ITOfilm with the same thickness is formed on the glass substrate, becausewhen the ITO film is formed directly on the dielectric multilayeredfilm, the ITO film and the dielectric multilayered film exhibit a coloras an integrated multilayered film, and thus the coloring is not onecreated by simply adding the color due to the ITO film and the color dueto the dielectric multilayered film.

Therefore, in order to perform display not only without coloringirregularities but also in achromatic color with flat spectroscopiccharacteristics, it is necessary to correct, by the first light controllayer on the visible side of the liquid crystal display panel 10′, thecoloring due to the constituting members in the liquid crystal displaypanel 10′ such as the transflective film 18 composed of the dielectricmultilayered film, the second electrode 6 composed of the ITO film, andso on during the reflection display.

For this purpose, in addition to the above-described function during thedisplay, it is preferable to further provide a function of coloringcorrection of correcting the coloring of light emitted from the liquidcrystal display panel 10′ to make almost flat the spectroscopiccharacteristics within the visible region, that is, to make thespectroscopic by adjusting, for example, the retardation value or theplacement direction of the slow axis 15 a of the first retardation film15. This arrangement can minimize the number of members to be provided,thereby reducing the cost.

Alternatively, it is also adoptable to provide another retardation filmfor coloring correction as a second light control layer.

In addition to the above, it is also possible to add a pigment to thefirst polarizing film 12 or to attach a color filter thereto to providecolor thereto, so as to provide a function of coloring correctionthereto.

Further, when the backlight 20 is provided to perform the transmissiondisplay as in this embodiment, it is necessary to correct the coloringduring the transmission display due to the constituting members in theliquid crystal display panel 10′ and the first light control layer, bythe second light control layer on the opposite side to the visible sideof the liquid crystal display panel 10′. This correction can beperformed through use of the second retardation film 17, the secondpolarizing film 14, or another retardation film or the like as in thecase of the first light control layer described above, and can beperformed, in addition to the above, by adjusting the coloring of thelight emitted from the backlight 20. The correction may be performed bycombination of these members.

The arrangement described above can easily realize achromatic displaywithout color irregularities. Further, in performing color display usingcolor filters of red (R), green (G), and blue (B), setting of opticalcharacteristics of each color filter for displaying an arbitrary colorcan be performed easily and accurately.

Note that the correction of coloring described above is similarlyapplicable also to the liquid crystal display device in the firstembodiment.

Besides, while the achromatic dielectric multilayered film is used inthe above-described liquid crystal display device of the secondembodiment, it is also possible to give an arbitrary color to thereflected light or transmitted light by adequately adjusting the filmthickness of each layer or the number of layers. It also applies to thecase in which the dielectric multilayered film behaves as the integratedmultilayered film, together with the ITO film formed thereon.Accordingly, it is also possible to realize achromatic display withalmost flat spectroscopic characteristics by performing theabove-described coloring correction through the adjustment of the filmthickness of each layer or the number of layers of the dielectricmultilayered film.

For example, the result of the simulation experiment by the presentinventors shows that in the case where the dielectric multilayered filmis formed in 2800 Å film thickness so that the color of passing light isa color in the red region within the luminosity range, when the secondelectrode 6 is formed on the dielectric multilayered film having theconfiguration shown in Table 1 used in this embodiment, the exhibitedcolor is almost achromatic with L* of 61.9, a* of 0.27, and b* of 18.4in the CIE 1976 color system.

Even in the case where the first electrode 5 is formed in 1800 Å filmthickness so that the color of passing light is a color in the blueregion within the luminosity range, the characteristics described abovecan be realized by adjusting the film thickness of each layer or thenumber of layers of the dielectric multilayered film.

Besides, when the color irregularities are reduced by setting the filmthickness of the first electrode 5 formed on the first substrate 1 onthe visible side to an appropriate value, the electrode and thedielectric multilayered film do not behave as an integrated multilayeredfilm, but achromatic display can be realized by establishing therelation so that the color exhibited by the ITO film and the colorexhibited by the dielectric multilayered film are complementary to eachother in this case.

It should be noted that while the liquid crystal display device providedwith the backlight 20 is described in the second embodiment, this is notan essential configuration. In addition, when the backlight is notprovided, there is also no need to provide the second retardation film17 and the second polarizing film 14 on the opposite side to the visibleside of the liquid crystal display panel 10′.

Further, while the example in which the transparent electrodes arecomposed of ITO is described in the above-described embodiments, theinvention is also applicable to the case in which the transparentelectrodes are composed using other materials. However, when using amember with a refractive index greatly different from that of ITO, theoptimal film thickness thereof will be different from those in theabove-described embodiments.

INDUSTRIAL APPLICABILITY

As has been described, with the liquid crystal display device of theinvention, the film thickness of at least one of the transparentelectrodes formed on the first and second substrates is set so that thecolor of light passing through the transparent electrode is a color inthe blue, purple or red region within the luminosity range, wherebycoloring irregularities within the display region of the liquid crystaldisplay device can be reduced and uniform display can be performed onthe entire surface. This can improve the display quality of the liquidcrystal display device.

This effect is particularly remarkable when the setting is applied tothe liquid crystal display device having a configuration in which thetransparent electrode is formed directly on the dielectric multilayeredfilm.

In addition, achromatic display without color irregularities can beperformed on the entire surface within the display region of the liquidcrystal display device by employing the first light control layer to beprovided on the visible side of the liquid crystal display panel, thesecond light control layer to be provided on the opposite side to thevisible side, or the auxiliary light source which has characteristics tocorrect, into achromatic color, the coloring of the light which isemitted from the liquid crystal display panel caused by the transparentelectrodes, the transflective film, or the like.

1. A liquid crystal display device comprising a liquid crystal displaypanel including a liquid crystal layer sandwiched between a firstsubstrate on a visible side and a second substrate on an opposite sideto the visible side having transparent electrodes on inner surfacesopposing to each other, wherein a transflective film formed of adielectric multilayered film made by alternately layering a highrefractive index film and a low refractive index film is providedbetween said second substrate and said transparent electrode on saidsecond substrate, wherein at least one of said transparent electrodesformed on said first and second substrates is colored, and whereinspectroscopic characteristics within a visible region of a reflectedlight or a transmitted light by said transflective film are almost flatthrough correction of coloring of light transmitted through said atleast one transparent electrode.
 2. The liquid crystal display deviceaccording to claim 1, wherein a film thickness of said at least one oftransparent electrodes is set so that light passing through saidtransparent electrode and exhibiting a maximum transmittance has a colorwithin either a region defined by an x value of 0.22 to 0.28 and a yvalue of 0.21 to 0.31 or a region defined by an x value of 0.28 to 0.34and a y value of 0.22 to 0.35 in a chromaticity diagram of a CIE 1931color system using a white light source.
 3. The liquid crystal displaydevice according to claim 2, wherein a first light control layer havingoptical anisotropy is provided on an opposite side to said liquidcrystal layer of said first substrate, and said first light controllayer has a characteristic of correcting coloring of light emitted fromsaid liquid crystal display panel to make spectroscopic characteristicsthereof within a visible region almost flat.
 4. The liquid crystaldisplay device according to claim 3, wherein an auxiliary light sourceplaced on an opposite side to said liquid crystal layer of said secondsubstrate; and a second light control layer having optical anisotropyplaced between said auxiliary light source and said second substrate,are provided respectively, and wherein either or both of said auxiliarylight source and said second light control layer has/have acharacteristic of correcting coloring of transmitting light emitted froma light source and transmitting through said liquid crystal displaypanel and said first light control layer to make spectroscopiccharacteristics within the visible region of the transmitting lightalmost flat.
 5. The liquid crystal display device according to claim 2,wherein said at least one transparent electrode is a transparentelectrode formed on said second substrate.
 6. The liquid crystal displaydevice according to claim 2, wherein said at least one transparentelectrode is 1600 Å to 2000 Å in film thickness.
 7. The liquid crystaldisplay device according to claim 2, wherein said at least onetransparent electrode is 2600 Å to 3000 Å in film thickness.